Hematologic and hemolysis studies were performed in 22 patients following xenograft atrioventricular valve replacements to evaluate the degree of hemolysis associated with these valves. Patients were studied 6-62 months postoperatively (mean 30.5 months). Preoperative mean hematologic values were: Hematocrit 39.4, reticulocyte index 1.3 percent, platelet count 281 x 10 to the 3rd power per cubic millimeter and LDH 234. The LDH was greater than 400 in five patients. The postoperative mean values were: Hematocrit 40.8, reticulocyte index 1.2 percent, platelet count 227 x 10 to the 3rd power/per cubic millimeter and LDH 204. Hemolysis studies including serum hemoglobin, and serum haptoglobin failed to indicate hemolysis in any patient. Postoperative iron studies were normal for the majority of patients. Only two patients had mild anemias, and their hemolysis studies were normal. Five patients had significantly elevated LDH values preoperatively which returned to normal following operation. Our evidence suggests that the glutaraldehyde fixed porcine xenograft provides excellent hemodynamic function without significant thromboembolism or chemically detectable hemolysis. Presently, it is our valve of choice for all atrioventricular replacements.